Vitex rotundifolia L. f. Engineered Microbial Interaction Reverse Desertification: Nitrogen-Fixing Consortia Drive Ecosystem Restoration in Sandy Wetlands of Poyang Lake

Background: The sandy areas of Poyang Lake are a typical region of wind erosion desertification in humid areas, and their ecological restoration urgently requires efficient, low-cost plant and microbial co-management measures. Vitex rotundifolia L. f., a local dominant pioneer shrub, has both medicinal and ecological value, but its mechanism of influence on sandy soil microorganisms remains unclear. To systematically assess how Vitex rotundifolia L. f. drives sand dune ecological restoration by altering soil physical and chemical properties and microbial community structure. Results: The total nitrogen (TN) and alkali-hydrolyzable nitrogen (AN) in the rhizosphere soil of Vitex rotundifolia L. f. grown for more than 3 years were 17-fold and 1.2-fold higher than those of bare sand, respectively. The activities of urease (UA) and nitrogenase (NA) significantly increased, while the moisture content slightly decreased. The bacterial α-diversity first increased and then slightly decreased, while fungal diversity decreased with increasing growth years. Cyanobacteria in the rhizosphere soil surged by 122-fold, while Actinobacteria and Proteobacteria increased by 1.3-fold and 1.4-fold, respectively. Fungi were dominated by Ascomycota and Basidiomycota. Functional prediction showed that nitrogen fixation, amino acid metabolism, and membrane transport pathways were significantly enriched. The proportion of wood-decaying fungi and ectomycorrhizal fungi increased, while pathogenic bacteria significantly decreased. Conclusion: Vitex rotundifoliaL. f. can significantly accelerate soil formation and ecological restoration of wet sand dunes in Poyang Lake by promoting nitrogen accumulation, constructing beneficial microbial communities, and forming biological crusts, providing a new strategy for low-cost and large-scale restoration of sandy land in humid areas.